Perfluoropolyether extraction processes

ABSTRACT

This disclosure relates to a process for extracting a perfluoropolyether. The process involves: (a) contacting a solvent comprising a liquid or supercritical carbon dioxide with a lubricating grease comprising a thickener and the perfluoropolyether in an extraction zone to form an extraction solution comprising an extracted perfluoropolyether; and (b) recovering the extracted perfluoropolyether from the extraction solution; wherein the recovered extracted perfluoropolyether comprises no more than about 2 wt % of the thickener.

BACKGROUND Field of the Disclosure

The present disclosure relates to a process for extracting and recovering a perfluoropolyether from a lubricating grease.

Description of Related Art

Perfluoropolyether (PFPE) oils are highly valued for properties including high-temperature performance, non-flammability, chemical inertness, superior stability and lubricity. Lubricating grease compounds, which possess similar properties, are created by combining the PFPE oil with a variety of thickeners and optionally other additives to meet the requirements of different applications.

Lubricating greases are manufactured so that the PFPE oil and the thickeners and other additives do not easily separate. This is extremely important in lubrication applications that experience high temperatures or high mechanical loads. An example of this requirement is in the aerospace industry which has adopted a military specification MIL-PRF-27617G that limits the amount of oil separation for various grades of grease. MIL-PRF-27617G Type II grease has a maximum allowance of oil separation of 15.0% when the grease is exposed to a temperature of 204° C. for a total of 30 hours. The oil separation is measured according to ASTM Method D6184 Standard Test Method for Oil Separation from Lubricating Grease.

Manufacturers that produce the lubricating grease compounds and the OEMS that consume the lubricating grease compounds generate waste streams of grease. The grease waste occurs during equipment cleanouts or during product transitions or during incomplete grease product removal from a package or other process steps that are common to manufacturing operations. The PFPE oil in the grease waste stream is not affected by contact with the additives or by the time in the waste stream, and the PFPE oil retains all of its valuable properties.

Therefore, there is a need to develop a cost-effective and environmentally-friendly process that is capable of separating the PFPE oil from the grease and recovering the oil for use.

BRIEF SUMMARY OF THE DISCLOSURE

The present disclosure provides a process for extracting a perfluoropolyether from a lubricating grease. The process comprises: (a) contacting a solvent comprising a liquid or supercritical carbon dioxide with the lubricating grease comprising a thickener and the perfluoropolyether in an extraction zone to form an extraction solution comprising an extracted perfluoropolyether; and (b) recovering the extracted perfluoropolyether from the extraction solution; wherein the recovered extracted perfluoropolyether comprises no more than about 2 wt % of the thickener.

BRIEF DESCRIPTION OF THE FIGURE

Embodiments are illustrated in the accompanying figures to improve understanding of concepts as presented herein.

FIG. 1 includes as illustration the extraction process flowsheet of custom high-pressure extraction apparatus.

FIG. 2 includes as illustration the extraction curve (extraction yield versus solvent to lubricating grease ratio, or solvent-to-feed ratio) for Example 1 at 3500 psig and 60° C.

FIG. 3 includes as illustration the extraction curve (extraction yield versus solvent to lubricating grease ratio, or solvent-to-feed ratio) for Example 2 at 4500 psig and 80° C.

FIG. 4 includes as illustration the extraction curve (extraction yield versus solvent to lubricating grease ratio, or solvent-to-feed ratio) for Example 3 at 1200 psig and 28° C.

FIG. 5 includes as illustration the extraction curve (extraction yield versus solvent to lubricating grease ratio, or solvent-to-feed ratio) for Example 4 at 2500 psig and 50° C.

Skilled artisans appreciate that objects in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the objects in the figures may be exaggerated relative to other objects to help to improve understanding of embodiments.

DETAILED DESCRIPTION

The foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as defined in the appended claims. Other features and benefits of any one or more of the embodiments will be apparent from the following detailed description, and from the claims.

As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Further, unless expressly stated to the contrary, “or” refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).

Also, use of “a” or “an” are employed to describe elements and components described herein. This is done merely for convenience and to give a general sense of the scope of the invention. This description should be read to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict, the present specification, including definitions, will control. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the present invention, suitable methods and materials are described below. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.

When an amount, concentration, or other value or parameter is given as either a range, preferred range or a list of upper preferable values and/or lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. Where a range of numerical values is recited herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range.

Before addressing details of embodiments described below, some terms are defined or clarified.

The term “wt %”, as used herein, means weight percent.

The term “extraction”, “extracted”, or “extracting”, as used herein, means a physical or chemical method of removing one or more components from a substrate by means of a solvent.

The term “extracted perfluoropolyether”, as used herein, means a perfluoropolyether that has been separated from the lubricating grease through extraction processes of this invention.

The term “lubricating grease”, as used herein, means the grease receiving the extraction processes of this invention to recover the PFPE oil contained therein. Typically, the lubricating grease comprises PFPE and one or more thickeners and other additives (if present, e.g., anti-corrosion additives) used in making such grease.

The term “yield of the extracted perfluoropolyether”, as used herein, means the amount of the extracted PFPE compared to the total amount of PFPE contained in the lubricating grease prior to extraction.

Supercritical Fluid

Supercritical fluids (SCF) exhibit properties intermediate between those of gases and liquids. A key feature of a SCF is that the fluid density can be varied continuously from liquid-like to gas-like densities by varying either the temperature or pressure, or a combination thereof. Various density-dependent physical properties likewise exhibit similar continuous variation in this region. Some of these properties include, but are not limited to, solvent strength (as evidenced by the solubilities of various substances in the SCF media), polarity, viscosity, diffusivity, heat capacity, thermal conductivity, isothermal compressibility, expandability, contractibility, fluidity, and molecular packing. The density variation in a SCF also influences the chemical potential of solutes and hence, reaction rates and equilibrium constants. Thus, the solvent environment in a SCF media can be optimized for a specific application by tuning the various density-dependent fluid properties.

A fluid is in the SCF state when the system temperature and pressure exceed the corresponding critical point values defined by the critical temperature (T_(c)) and pressure (P_(c)). For pure substances, the T_(c) and P_(c) are the highest at which vapor and liquid phases can coexist. Above the T_(c), a liquid does not form for a pure substance, regardless of the applied pressure. Similarly, the P_(c) and critical molar volume are defined at this T_(c) corresponding to the state at which the vapor and liquid phases merge. For carbon dioxide, the critical point is 7.38 MPa (P_(c)) at 31.1° C. (T_(c)). For a discussion of supercritical fluids, see Kirk-Othmer Encycl. of Chem. Technology, 4th Ed., Vol. 23, pg. 452-477.

Perfluoropolyethers

Perfluoropolyethers are oligomers or polymers composed of perfluoroalkyl ether repeating units. A perfluoropolyether is typically polydisperse, a mixture of oligomers or polymers with different molecular weights. Perfluoropolyether is synonymous to perfluoropolyalkylether. Other synonymous terms frequently used include “PFPE”, “PFAE”, “PFPE Oil”, “PFPE fluid”, and “PFPAE”. These synonyms can be used interchangeably in this disclosure. The two end groups of a suitable perfluoropolyether for the processes of this invention, independently, can be functionalized or unfunctionalized. In an unfunctionalized perfluoropolyether, the end group can be branched or straight chain perfluoroalkyl radical end groups. Examples of such perfluoropolyethers can have the formula of C_(r′)F_((2r′+1))-A-C_(r′)F_((2r′+1)) in which each r′ is independently 3 to 6; A can be O—(CF(CF₃)CF₂—O)_(w′), O—(CF₂—O)_(x′)(CF₂CF₂—O)_(y′), O—(C₂F₄—O)_(w′), O—(C₂F₄—O)_(x′)(C₃F₆—O)_(y′), O—(CF(CF₃)CF₂—O)_(x′)(CF₂—O)_(y′), O—(CF₂CF₂CF₂—O)_(w′), O—(CF(CF₃)CF₂—O)_(x′)(CF₂CF₂—O)_(y′)—(CF₂—O)_(z′), or combinations of two or more thereof; preferably A is O—(CF(CF₃)CF₂—O)_(w′), O—(C₂F₄—O)_(w′), O—(C₂F₄—O)_(x′)(C₃F₆—O)_(y′), O—(CF₂CF₂CF₂—O)_(w′), or combinations of two or more thereof; w′ is an integer from 4 to 100; x′ and y′ are each independently an integer from 1 to 100. Specific examples include, but are not limited to, F(CF(CF₃)—CF₂—O)₉—CF₂CF₃, F(CF(CF₃)—CF₂—O)₉—CF(CF₃)₂, and combinations thereof. In such PFPEs, up to 30% of the halogen atoms can be halogens other than fluorine, such as, for example, chlorine atoms.

In some embodiments of this invention, the lubricating grease comprises a perfluoropolyether wherein at least one end group of the perfluoropolyether is unfunctionalized. In some embodiments, such an unfunctionalized end group is a branched or straight chain perfluoroalkyl group. In some embodiments, such an unfunctionalized end group is a straight chain perfluoroalkyl group.

The two end groups of a suitable perfluoropolyether for the processes of this invention, independently, can also be functionalized. A typical functionalized end group can be selected from the group consisting of esters, hydroxyls, amines, amides, cyanos, carboxylic acids and sulfonic acids. In some embodiments of this invention, these functionalized perfluoropolyethers are added to the fully inert PFPE fluids as anti-corrosion, anti-wear, or extreme pressure additives in an amount of no more than about 10 wt %, and in some embodiments no more than about 3 wt %, compared to the total amount of PFPE fluid.

Representative perfluoropolyethers suitable for the processes of this invention include KRYTOX® fluids which are available from DuPont and have the formula of CF₃—(CF₂)₂—O—[CF(CF₃)—CF₂—O]_(j′)—R′f. In the formula, j′ is an integer from 2-100 and R′f is CF₂CF₃, a C₃ to C₆ perfluoroalkyl group, or combinations thereof.

Representative perfluoropolyethers suitable for the processes of this invention also include FOMBLIN® and GALDEN® fluids, available from Ausimont, Milan, Italy and produced by perfluoroolefin photooxidation. For example, FOMBLIN®-Y can have the formula of CF₃O[CF₂CF(CF₃)O]_(m)(CF₂O)_(n)—R_(1f) or CF₃O[CF₂CF(CF₃)O]_(m′)(CF₂CF₂O)_(o′)(CF₂O)_(n′)—R_(1f). In the formulae R_(1f) is CF₃, C₂F₅, C₃F₇, or combinations of two or more thereof; (m+n) is an integer from 8-45; and m/n is from 20-1000; o′ is 1; (m′+n′+o′) is an integer from 8-45; m′/n′ is from 20-1000. FOMBLIN®-Z can have the formula of CF₃O(CF₂CF₂—O—)_(p′)(CF₂—O)_(q′)CF₃ where (p′+q′) is an integer from 40-180 and p′/q′ is from 0.5-2.

Representative perfluoropolyethers suitable for the processes of this invention also include DEMNUM® fluids, another family of PFPE available from Daikin Industries. It can be produced by sequential oligomerization and fluorination of 2,2,3,3-tetrafluorooxetane, yielding the formula of F—[(CF₂)₃—O]_(t′)—R_(2f) where R_(2f) is CF₃, C₂F₅, or combinations thereof and t′ is an integer from 2-200.

Lubricating Grease

A lubricating grease receiving the extraction processes of this invention typically comprises, other than PFPE, one or more thickeners and optionally one or more other additives such as anti-corrosion additives, anti-rust additives, or anti-wear additives. In some embodiments of this invention, the lubricating grease comprises, consists essentially of, or consists of a thickener and a perfluoropolyether.

Thickeners for a lubricating grease include, but are not limited to, one or more of the following materials: halogenated polymers and co-polymers such as polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), perfluoroalkoxy (PFA), perfluoro methyl alkoxy (MFA), ethylene tetrafluoroethylene (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene chlorotrifluoroethylene (ECTFE), polyvinylidene fluoride (PVDF), and the like, talc, silica, clay, boron nitride, titanium dioxide, silicon nitride, metal soaps such as lithium soaps, sodium soaps, lithium complex soaps, calcium sulfonates, aluminum soaps, and the like, melamine cyanurate, urea, polyureas, polyurethanes, and polyolefins such as polyethylene. In some embodiments, the silica thickener is a fumed silica. The thickeners can be present in any appropriate molecular weight distributions, particle shapes and sizes as known to one skilled in the art. For example, the polytetrafluoroethylene thickener can be polytetrafluoroethylene micropowder.

In some embodiments of this invention, the thickener is a halogenated polymer or co-polymer. In some embodiments of this invention, the thickener is selected from the group consisting of PTFE, FEP, PFA, MFA, ETFE, PCTFE, ECTFE, PVDF, and combinations thereof. In some embodiments of this invention, the thickener is PTFE.

In some embodiments of this invention, the thickener is an inorganic compound. In some embodiments of this invention, the thickener is selected from the group consisting of talc, silica, clay, boron nitride, titanium dioxide, silicon nitride, and combinations thereof.

In some embodiments of this invention, the thickener is an organic compound. In some embodiments of this invention, the thickener is selected from the group consisting of metal soaps, melamine cyanurate, urea, polyureas, polyurethanes, polyolefins, and combinations thereof.

In some embodiments of this invention, the metal soap is selected from the group consisting of lithium soaps, sodium soaps, lithium complex soaps, calcium sulfonates, aluminum soaps, and combinations thereof.

In some embodiments of this invention, the lubricating grease further comprises, other than PFPE and thickener, one or more other additives such as anti-corrosion additives, anti-rust additives, or anti-wear additives. Examples of such other additives include sodium nitrite and organic phosphorus compounds.

Extraction and Recovery

The present disclosure provides a process for extracting a perfluoropolyether. The process comprises: (a) contacting a solvent comprising a liquid or supercritical carbon dioxide with a lubricating grease comprising a thickener and the perfluoropolyether in an extraction zone to form an extraction solution comprising an extracted perfluoropolyether; and (b) recovering the extracted perfluoropolyether from the extraction solution; wherein the recovered extracted perfluoropolyether comprises no more than about 2 wt % of the thickener.

It was found through experiments that perfluoropolyethers contained in a lubricating grease can be efficiently separated and recovered from the grease by using liquid or supercritical carbon dioxide as the extracting solvent. The process is cost-effective and environmentally friendly.

In some embodiments of this invention, the yield of the extracted perfluoropolyether is at least about 75 wt %. In some embodiments, the yield of the extracted perfluoropolyether is at least about 80 wt %. In some embodiments, the yield of the extracted perfluoropolyether is at least about 85 wt %. In some embodiments, the yield of the extracted perfluoropolyether is at least about 90 wt %. In some embodiments, the yield of the extracted perfluoropolyether is at least about 95 wt %. In some embodiments, the yield of the extracted perfluoropolyether is at least about 99 wt %.

A suitable solvent for the extraction processes of this invention comprises, consists essentially of, or consists of a liquid carbon dioxide or a supercritical carbon dioxide.

In some embodiments of this invention, the solvent comprises, consists essentially of, or consists of a liquid carbon dioxide. In some embodiments, the solvent consists essentially of a liquid carbon dioxide.

In some embodiments of this invention, the solvent comprises, consists essentially of, or consists of a supercritical carbon dioxide. In some embodiments, the solvent consists essentially of a supercritical carbon dioxide.

In some embodiments of this invention, the weight ratio of the solvent to the lubricating grease is no more than about 50. In some embodiments of this invention, the weight ratio of the solvent to the lubricating grease is no more than about 30. In some embodiments, the weight ratio of the solvent to the lubricating grease is no more than about 10. In some embodiments, the weight ratio of the solvent to the lubricating grease is no more than about 8. In some embodiments, the weight ratio of the solvent to the lubricating grease is no more than about 7. In some embodiments, the weight ratio of the solvent to the lubricating grease is no more than about 6. In some embodiments, the weight ratio of the solvent to the lubricating grease is no more than about 5.

In some embodiments of this invention, the weight ratio of the solvent to the lubricating grease is no more than about 7, and the yield of the extracted perfluoropolyether is at least about 75 wt %, at least about 90 wt %, or at least about 95 wt %. In some embodiments of this invention, the solvent comprises, consists essentially of, or consists of a supercritical carbon dioxide, the weight ratio of the solvent to the lubricating grease is no more than about 7, the temperature in the extraction zone is from about 40° C. to about 100° C., the pressure in the extraction zone is from about 2200 psig to about 6000 psig, and the yield of the extracted perfluoropolyether is at least about 90 wt % or at least about 95 wt %.

The contacting step (a) can be carried out using well-known chemical engineering practices in an extraction vessel. In some embodiments of this invention, a lubricating grease is placed in a container through which the liquid or supercritical carbon dioxide is passed to solubilize the PFPE contained in the lubricating grease to form an extraction solution. The liquid or supercritical carbon dioxide can flow through the lubricating grease continuously, or be exposed to the lubricating grease in a discontinuous batch process.

The extraction vessel can be made of materials known in the art. In some embodiments of this invention, the extraction vessel is a stainless steel, high pressure vessel. In some embodiments of this invention, the extraction vessel is a vertical column and is operated in an upflow or downflow configuration. In some embodiments, the solvent is fed to the extraction zone in an upflow mode. In some embodiments, the solvent is fed to the extraction zone in a downflow mode.

The temperature and pressure in the extraction zone are chosen to keep the carbon dioxide in the liquid or supercritical state during the extraction process.

When the solvent comprises, consists essentially of, or consists of a supercritical carbon dioxide, typically the temperature in the extraction zone is from T_(c) to no more than about 150° C. In some embodiments, the temperature is from about 40° C. to about 110° C. In some embodiments, the temperature is from about 50° C. to about 100° C. In some embodiments, the temperature is from about 60° C. to about 90° C. In some embodiments, the temperature is from about 70° C. to about 90° C. Typically, the pressure in the extraction zone is from about 1500 psig to about 10,000 psig. In some embodiments, the pressure is from about 1500 psig to about 6000 psig. In some embodiments, the pressure is from about 2000 psig to about 6000 psig. In some embodiments, the pressure is from about 3000 psig to about 5000 psig. In some embodiments, the pressure is from about 4000 psig to about 5000 psig.

When the solvent comprises, consists essentially of, or consists of a liquid carbon dioxide, typically the temperature in the extraction zone is from about 0° C. to less than T_(c). In some embodiments, the temperature is from about 15° C. to less than T_(c). In some embodiments, the temperature is from about 25° C. to less than T_(c).

The extraction solution obtained from the contacting step typically comprises the solvent (i.e., liquid or supercritical carbon dioxide), the extracted perfluoropolyether, water, and the thickener contaminant.

In the recovering step (b), the extracted perfluoropolyether can be recovered from the extraction solution. In some embodiments of this invention, the extracted perfluoropolyether is recovered from the extraction solution by evaporating the liquid or supercritical carbon dioxide. As the liquid or supercritical carbon dioxide evaporates, the extracted perfluoropolyether is typically precipitated out together with water and the thickener contaminant contained in the extraction solution.

It was found through experiments that PFPE can be effectively separated from the lubricating grease substantially free of thickeners and other additives. In some embodiments of this invention, the recovered extracted perfluoropolyether comprises no more than about 2 wt % of the thickener. In some embodiments of this invention, the recovered extracted perfluoropolyether comprises no more than about 1 wt % of the thickener. In some embodiments of this invention, the recovered extracted perfluoropolyether comprises no more than about 0.1 wt % of the thickener. In this disclosure, the sentence “recovered extracted perfluoropolyether comprises no more than about 2 wt % of the thickener” means that the amount of the thickener contaminant contained in the recovered extracted perfluoropolyether is no more than about 2 wt % compared to the total amount of the pure perfluoropolyether and the thickener contained in the recovered extracted perfluoropolyether.

In some embodiments of this invention, the extraction solution is directed through a pressure reduction valve to a separation vessel where the liquid or supercritical carbon dioxide is evaporated and removed and the extracted perfluoropolyether is precipitated from the extraction solution for collection. The relatively pure CO₂ stream from the top of the separation vessel may be recycled back to the extraction zone.

In some embodiments of this invention, the recovered extracted perfluoropolyethers can be further purified as described in this disclosure.

Purification

Water and other contaminants in the recovered extracted perfluoropolyether can be removed by techniques known in the art. In some embodiments, water and the extracted perfluoropolyether will separate into two phases, and water can be removed by, for example, simple decantation. In some embodiments, water can be removed by drying agents such as molecular sieves.

In some embodiments of this invention, the recovered extracted perfluoropolyether can be purified by contacting with an adsorbing agent, such as activated carbon, diatomaceous earth, or alumina, to remove the discoloration contaminants. The activated carbon can be in the form of powder, granules, or pellets, et al. Commercially available diatomaceous earth include those sold under the Celite® trademark name.

Activated carbon used in the embodiments of this invention may come from any of the following sources: wood, peat, coal, coconut shells, bones, lignite, petroleum-based residues and sugar. Commercially available activated carbons which may be used include those sold under the following trademarks: Barneby & Sutcliffe™, Darco™, Nucharm, Columbia JXN™, Columbia LCK™, Calgon™ PCB, Calgon™ BPL, Westvaco™, Norit™, Takeda™ and Barnaby Cheny NB™.

The activated carbon also includes three dimensional matrix porous carbonaceous materials. Examples are those described in U.S. Pat. No. 4,978,649. In one embodiment of the invention, activated carbon includes three dimensional matrix carbonaceous materials which are obtained by introducing gaseous or vaporous carbon-containing compounds (e.g., hydrocarbons) into a mass of granules of a carbonaceous material (e.g., carbon black); decomposing the carbon-containing compounds to deposit carbon on the surface of the granules; and treating the resulting material with an activator gas comprising steam to provide a porous carbonaceous material. A carbon-carbon composite material is thus formed.

In some embodiments, the purified extracted perfluoropolyether can be fractionated or distilled to generate perfluoropolyether with desired molecular weight. The purified extracted perfluoropolyether can also undergo chemical reactions to produce PFPE oil with desired properties.

Many aspects and embodiments have been described above and are merely exemplary and not limiting. After reading this specification, skilled artisans appreciate that other aspects and embodiments are possible without departing from the scope of the invention.

EXAMPLES

The concepts described herein will be further described in the following examples, which do not limit the scope of the invention described in the claims.

Materials: Eleven grades of formulated perfluoropolyether lubricating greases were used in these examples, including commercially-available DuPont Krytox® greases and non-commercial research samples to illustrate the breadth of the applicability of this extraction process at recovering perfluoropolyether oil from various grease matrix formulations.

-   -   Krytox® GPL 203: 15-45% PTFE Micropowder and 55-85% PFPE Oil     -   Krytox® GPL 207: 15-45% PTFE Micropowder and 55-85% PFPE Oil     -   Krytox® GPL 227: 18-27% PTFE Micropowder, 1-5% Sodium Nitrite         and 71-80% PFPE Oil     -   Krytox® GPL226SR: 23-25% PTFE Micropowder, 2-3% of a proprietary         additive, and 73-74% PFPE oil     -   Krytox® NRT 8908: 30-50% Talc (Mg₃H₂(SiO₃)₄) and 50-70% PFPE oil     -   Krytox® GPL 407: 1-10% Silica and 90-95% PFPE Oil     -   XHT-BD: 15-25% Boron Nitride, and 75-85% PFPE oil     -   Mg Stearate:GPL205: 15-45% Mg Stearate powder and 55-85% PFPE         oil     -   BN/PTFE:GPL205: 10-40% Micropowder consisting of 50 wt % Boron         Nitride/50 wt % PTFE thickener and 6-85% PFPE oil     -   PU: 15-45% Polyurea thickener and 35-45% PFPE oil     -   PU/ZnO: 15-45% Polyurea+zinc oxide thickener and 35-45% PFPE oil

Carbon dioxide (99.99% grade) was obtained from GTS-Welco.

Extraction Method: The extraction examples were conducted using a custom high-pressure extraction apparatus illustrated in FIG. 1. The 300 mL extraction vessel (High Pressure Equipment Co.) was fabricated from 316 SS and was equipped with a 2-micron sintered metal filter on the effluent end of the vessel. The extraction vessel was fitted with band heating elements (Power Modules, Inc.) which were controlled by an automated temperature controller monitoring a thermocouple imbedded in the extraction vessel wall. The vessel was equipped with an insulation blanket to maintain a uniform extraction temperature. The CO₂ was supplied from a standard cylinder with the CO₂ vapor from the top of the cylinder condensed and chilled to 5° C. in a heat exchanger and fed into one of two positive displacement syringe pumps (Isco Model 100D/X) for metering into the extraction vessel. The CO₂ pumps were interconnected via a dual-pump valve kit (ISCO Model DP VK) and operated in continuous flow mode. Prior to entering the top of the extraction vessel, the inlet CO₂ stream was preheated by an electrical heating tape (Amptek AWH-051) wrapped around the transfer tubing which was operated via an automated temperature controller. The extraction temperature was monitored and controlled from three calibrated thermocouples (Omega Engineering Inc., Type K) located at the extraction vessel inlet, inside the extraction vessel, and at the extraction vessel outlet. The extraction pressure was maintained with an automated back pressure regulator (Jasco Model BP-1580-81) on the effluent side of the vessel, and the extracted perfluoropolyether oil was collected in a sample vessel while simultaneously venting the CO₂ solvent to the atmosphere.

For each example, an approximately 100-200 g quantity of the starting lubricating grease was weighed into two perforated metal baskets custom made to fit into the 300 mL extraction vessel. After placing these baskets into the extraction vessel, the system was sealed, heated, and pressurized at the desired CO₂ flow rate to the desired operating conditions. The back pressure regulator was then set to the desired operating pressure. The time, pressure, temperature, recovered PFPE oil weight, and total CO₂ liquid volume fed from the syringe pumps were monitored during the extraction. When the desired extraction time was complete, a pre-programmed 2 hr depressurization routine was initiated on the back pressure regulator to reduce the system to atmospheric pressure. The baskets were then removed and weighed. Reported extraction yields from the starting lubricating grease samples were determined gravimetrically based on the total amount of PFPE oil contained in the starting lubricating greases.

The following examples show quantitative results for semi-continuous CO₂ extractions of the eleven DuPont Krytox® lubricating grease samples under various conditions to exemplify the technical feasibility of this process approach for separating the Krytox® PFPE oil from the lubricating grease matrix.

Example 1 Extraction Curve at 3500 Psig and 60° C. Using Supercritical CO₂ with Krytox® GPL 207 Lubricating Grease

This Example demonstrated the feasibility of isolating perfluoropolyether oil from a PTFE-based lubricating grease matrix with supercritical CO₂ at extraction conditions of 3500 psig and 60° C. and illustrated generation of an extraction curve showing the relative amount of PFPE oil recovered as a function of the solvent (CO₂)-to-feed (lubricating grease) ratio at the given extraction conditions.

A 300 mL extraction vessel was charged with 234.2 g of DuPont Krytox® GPL 207 lubricating grease which was placed in two perforated metal baskets in the vessel. The extraction vessel and lubricating grease sample were flushed with CO₂ and then pressurized to 3500 psig with CO₂ at 60° C. The lubricating grease sample was extracted at these conditions and a CO₂ flow rate of 2.0 g/m in for 9 h with intermittent PFPE oil samples collected from the extract. Table 1 shows the corresponding cumulative extraction yield as a function of the cumulative solvent-to-feed ratio, and this trend is further illustrated in FIG. 2. A total of 75.2 wt % of the 185.2 g of PFPE oil in the starting lubricating grease was recovered in the extract with a total cumulative solvent-to-feed ratio of 6.36. FT-IR and ¹⁹F NMR analysis verified the recovered PFPE oils to be structurally identical to the original PFPE oils in the starting lubricating grease.

TABLE 1 Solvent-to-Feed Ratio and Extraction Yield Data at 3500 psig and 60° C. for Example 1 Specific Solvent Ratio Extraction Yield (g CO₂/g Lubricating Grease) (wt %) 0.13 6.0 0.32 13.1 0.58 23.6 1.09 37.2 1.60 46.3 2.15 52.8 2.92 59.2 3.69 64.2 4.46 68.2 5.32 72.0 6.36 75.2

Example 2 Extraction Curve at 4500 Psig and 80° C. Using Supercritical CO₂ with Krytox® GPL 227 Lubricating Grease

This Example demonstrated the feasibility of isolating perfluoropolyether oil from a PTFE-based lubricating grease matrix with supercritical CO₂ at extraction conditions of 4500 psig and 80° C.

A 300 mL extraction vessel was charged with 232.5 g of DuPont Krytox® GPL 227 lubricating grease which was placed in two perforated metal baskets in the vessel. The extraction vessel and lubricating grease sample were flushed with CO₂ and then pressurized to 4500 psig with CO₂ at 80° C. The lubricating grease sample was extracted at these conditions and a CO₂ flow rate of 2.1 g/m in for 9 h with intermittent PFPE oil samples collected from the extract. Table 2 shows the corresponding cumulative extraction yield as a function of the cumulative solvent-to-feed ratio, and this trend is further illustrated in FIG. 3. A total of 95.1 wt % of the 183.4 g of PFPE oil in the starting lubricating grease was recovered in the extract with a total cumulative solvent-to-feed ratio of 6.54. FT-IR and ¹⁹F NMR analysis verified the recovered PFPE oils to be structurally identical to the original PFPE oils in the starting lubricating grease.

TABLE 2 Solvent-to-Feed Ratio and Extraction Yield Data at 4500 psig and 80° C. for Example 2 Specific Solvent Ratio Extraction Yield (g CO₂/g Lubricating Grease) (wt %) 0.20 16.1 0.37 23.4 0.62 35.8 1.15 50.6 1.71 61.7 2.24 69.5 2.90 77.2 3.55 82.6 4.27 87.1 5.48 92.1 6.54 95.1

Example 3 Extraction Curve at 1200 Psig and 28° C. Using Liquid CO₂ with Krytox® GPL 203 Lubricating Grease

This Example demonstrated the feasibility of isolating perfluoropolyether oil from a PTFE-based lubricating grease matrix with liquid CO₂ at extraction conditions of 1200 psig and 28° C.

A 300 mL extraction vessel was charged with 229.7 g of DuPont Krytox® GPL 203 lubricating grease which was placed in two perforated metal baskets in the vessel. The extraction vessel and lubricating grease sample were flushed with CO₂ and then pressurized to 1200 psig with liquid CO₂ at 28° C. The lubricating grease sample was extracted at these conditions and a CO₂ flow rate of 1.8 g/m in for 2.7 h with intermittent PFPE oil samples collected from the extract. Table 3 shows the corresponding cumulative extraction yield as a function of the cumulative solvent-to-feed ratio, and this trend is further illustrated in FIG. 4. A total of 45.0 wt % of the 177.0 g of PFPE oil in the starting lubricating grease was recovered in the extract with a total cumulative solvent-to-feed ratio of 1.76. FT-IR and ¹⁹F NMR analysis verified the recovered PFPE oils to be structurally identical to the original PFPE oils in the starting lubricating grease.

TABLE 3 Solvent-to-Feed Ratio and Extraction Yield Data at 1200 psig and 28° C. for Example 3 Specific Solvent Ratio Extraction Yield (g CO₂/g Lubricating Grease) (wt %) 0.09 4.7 0.17 8.5 0.33 15.1 0.47 20.2 0.64 25.7 0.84 30.8 1.04 34.7 1.28 38.7 1.54 42.1 1.76 45.0

Example 4 Extraction Curve at 2500 Psig and 50° C. Using Supercritical CO₂ with Krytox® GPL 227 Lubricating Grease

This Example demonstrated the feasibility of isolating perfluoropolyether oil from a PTFE-based lubricating grease matrix with supercritical CO₂ at extraction conditions of 2500 psig and 50° C.

A 300 mL extraction vessel was charged with 208.0 g of DuPont Krytox® GPL 227 lubricating grease which was placed in two perforated metal baskets in the vessel. The extraction vessel and lubricating grease sample were flushed with CO₂ and then pressurized to 2500 psig with CO₂ at 50° C. The lubricating grease sample was extracted at these conditions and a CO₂ flow rate of 1.9 g/m in for 5.9 h with intermittent PFPE oil samples collected from the extract. Table 4 shows the corresponding cumulative extraction yield as a function of the cumulative solvent-to-feed ratio, and this trend is further illustrated in FIG. 5. A total of 50.8 wt % of the 164.0 g of PFPE oil in the starting lubricating grease was recovered in the extract with a total cumulative solvent-to-feed ratio of 4.7. FT-IR and ¹⁹F NMR analysis verified the recovered PFPE oils to be structurally identical to the original PFPE oils in the starting lubricating grease.

TABLE 4 Solvent-to-Feed Ratio and Extraction Yield Data at 2500 psig and 50° C. for Example 4 Specific Solvent Ratio Extraction Yield (g CO₂/g Lubricating Grease) (wt %) 0.10 1.6 0.16 3.5 0.31 6.7 0.39 9.2 0.50 12.1 0.77 18.6 1.09 24.8 1.55 29.6 2.01 33.7 2.64 38.7 3.05 41.7 3.57 45.0 3.83 46.5 4.70 50.8

Example 5 Extraction Curve at 4500 Psig and 80° C. Using Supercritical CO₂ with Krytox® GPL 226SR Lubricating Grease

This Example demonstrated the feasibility of isolating perfluoropolyether oil from a PTFE Micropowder-based lubricating grease matrix containing a proprietary additive with supercritical CO₂ at extraction conditions of 4500 psig and 80° C.

A 300 mL extraction vessel was charged with 102.9 g of DuPont Krytox® GPL 226SR lubricating grease which was placed in two perforated metal baskets in the vessel. The extraction vessel and lubricating grease sample were flushed with CO₂ and then pressurized to 4500 psig with CO₂ at 80° C. The lubricating grease sample was extracted at these conditions and a CO₂ flow rate of 5.2 g/m in for 3.7 h with intermittent PFPE oil samples collected from the extract. Table 5 shows the corresponding cumulative extraction yield as a function of the cumulative solvent-to-feed ratio. A total of 95.5 wt % of the 77.7 g of PFPE oil in the starting lubricating grease was recovered in the extract with a total cumulative solvent-to-feed ratio of 11.1. FT-IR analysis verified the recovered PFPE oils to be structurally identical to the original PFPE oils in the starting lubricating grease.

TABLE 5 Solvent-to-Feed Ratio and Extraction Yield Data at 4500 psig and 80° C. for Example 5 Specific Solvent Ratio Extraction Yield (g CO₂/g Lubricating Grease) (wt %) 0.25 17.3 0.50 23.2 0.75 27.9 1.26 35.8 2.01 46.6 3.02 57.5 4.02 66.4 5.08 73.3 7.04 82.1 9.05 88.6 10.1 90.9 11.1 95.5

Example 6 Extraction Curve at 4500 Psig and 80° C. Using Supercritical CO₂ with Krytox® NRT 8908 Lubricating Grease

This Example demonstrated the feasibility of isolating perfluoropolyether oil from a talc-based lubricating grease matrix with supercritical CO₂ at extraction conditions of 4500 psig and 80° C.

A 300 mL extraction vessel was charged with 172.7 g of DuPont Krytox® NRT 8908 lubricating grease which was placed in two perforated metal baskets in the vessel. The extraction vessel and lubricating grease sample were flushed with CO₂ and then pressurized to 4500 psig with CO₂ at 80° C. The lubricating grease sample was extracted at these conditions and a CO₂ flow rate of 5.2 g/m in for 4.4 h with intermittent PFPE oil samples collected from the extract. Table 6 shows the corresponding cumulative extraction yield as a function of the cumulative solvent-to-feed ratio. A total of 92.9 wt % of the 120.9 g of PFPE oil in the starting lubricating grease was recovered in the extract with a total cumulative solvent-to-feed ratio of 7.9. FT-IR analysis verified the recovered PFPE oils to be structurally identical to the original PFPE oils in the starting lubricating grease.

TABLE 6 Solvent-to-Feed Ratio and Extraction Yield Data at 4500 psig and 80° C. for Example 6 Specific Solvent Ratio Extraction Yield (g CO₂/g Lubricating Grease) (wt %) 0.15 7.9 0.30 13.1 0.60 22.9 0.90 33.5 1.35 42.3 1.80 49.8 2.40 57.8 2.99 64.3 4.19 73.8 5.39 80.6 6.29 84.4 7.04 86.9 7.94 92.9

Example 7 Extraction Curve at 4500 Psig and 80° C. Using Supercritical CO₂ with Krytox® GPL 407 Lubricating Grease

This Example demonstrated the feasibility of isolating perfluoropolyether oil from a silica-based lubricating grease matrix with supercritical CO₂ at extraction conditions of 4500 psig and 80° C.

A 300 mL extraction vessel was charged with 146.7 g of DuPont Krytox® GPL 407 lubricating grease which was placed in two perforated metal baskets in the vessel. The extraction vessel and lubricating grease sample were flushed with CO₂ and then pressurized to 4500 psig with CO₂ at 80° C. The lubricating grease sample was extracted at these conditions and a CO₂ flow rate of 5.2 g/m in for 4.2 h with intermittent PFPE oil samples collected from the extract. Table 7 shows the corresponding cumulative extraction yield as a function of the cumulative solvent-to-feed ratio. A total of 97.2 wt % of the 139.74 g of PFPE oil in the starting lubricating grease was recovered in the extract with a total cumulative solvent-to-feed ratio of 8.8. FT-IR analysis verified the recovered PFPE oils to be structurally identical to the original PFPE oils in the starting lubricating grease.

TABLE 7 Solvent-to-Feed Ratio and Extraction Yield Data at 4500 psig and 80° C. for Example 7 Specific Solvent Ratio Extraction Yield (g CO₂/g Lubricating Grease) (wt %) 0.17 23.2 0.35 32.8 0.53 39.9 0.88 52.2 1.23 61.5 1.76 68.2 2.29 73.5 3.00 79.3 4.16 85.6 5.47 90.1 6.53 92.6 7.24 93.9 8.82 97.2

Example 8 Extraction Curve at 4500 Psig and 80° C. Using Supercritical CO₂ with Krytox® XHT-BD Lubricating Grease

This Example demonstrated the feasibility of isolating perfluoropolyether oil from a Boron Nitride-based lubricating grease matrix with supercritical CO₂ at extraction conditions of 4500 psig and 80° C.

A 300 mL extraction vessel was charged with 150.3 g of DuPont Krytox® XHT-BD lubricating grease which was placed in two perforated metal baskets in the vessel. The extraction vessel and lubricating grease sample were flushed with CO₂ and then pressurized to 4500 psig with CO₂ at 80° C. The lubricating grease sample was extracted at these conditions and a CO₂ flow rate of 5.2 g/m in for 4.2 h with intermittent PFPE oil samples collected from the extract. Table 8 shows the corresponding cumulative extraction yield as a function of the cumulative solvent-to-feed ratio. A total of 89.5 wt % of the 117.0 g of PFPE oil in the starting lubricating grease was recovered in the extract with a total cumulative solvent-to-feed ratio of 8.6. FT-IR analysis verified the recovered PFPE oils to be structurally identical to the original PFPE oils in the starting lubricating grease.

TABLE 8 Solvent-to-Feed Ratio and Extraction Yield Data at 4500 psig and 80° C. for Example 8 Specific Solvent Ratio Extraction Yield (g CO₂/g Lubricating Grease) (wt %) 0.17 18.3 0.34 25.2 0.52 29.9 0.86 38.3 1.21 45.4 1.72 51.4 2.24 56.6 2.93 62.8 4.06 70.6 5.34 77.1 6.37 81.1 7.06 83.3 8.61 89.5

Example 9 Extraction Curve at 4500 Psig and 80° C. Using Supercritical CO₂ with Magnesium Stearate-Thickened Krytox® GPL205 Lubricating Grease

This Example demonstrated the feasibility of isolating perfluoropolyether oil from a Magnesium Stearate-based lubricating grease matrix with supercritical CO₂ at extraction conditions of 4500 psig and 80° C.

A 300 mL extraction vessel was charged with 154.7 g of a lubricating grease comprised of magnesium stearate and DuPont Krytox® GPL205 PFPE oil which was placed in two perforated metal baskets in the vessel. The extraction vessel and lubricating grease sample were flushed with CO₂ and then pressurized to 4500 psig with CO₂ at 80° C. The lubricating grease sample was extracted at these conditions and a CO₂ flow rate of 5.2 g/min for 3.6 h with intermittent PFPE oil samples collected from the extract. Table 9 shows the corresponding cumulative extraction yield as a function of the cumulative solvent-to-feed ratio. A total of 99.8 wt % of the 126.9 g of PFPE oil in the starting lubricating grease was recovered in the extract with a total cumulative solvent-to-feed ratio of 7.2. FT-IR analysis verified the recovered PFPE oils to be structurally identical to the original PFPE oils in the starting lubricating grease.

TABLE 9 Solvent-to-Feed Ratio and Extraction Yield Data at 4500 psig and 80° C. for Example 9 Specific Solvent Ratio Extraction Yield (g CO₂/g Lubricating Grease) (wt %) 0.17 13.4 0.33 19.7 0.50 24.8 0.83 34.7 1.17 42.2 1.67 52.4 2.17 62.4 3.04 76.0 3.94 85.4 4.88 91.9 6.25 97.0 7.19 99.8

Example 10 Extraction Curve at 4500 Psig and 80° C. Using Supercritical CO₂ with 50 wt % Boron Nitride/50 wt % PTFE Micropowder-Thickened Krytox® GPL205 Lubricating Grease

This Example demonstrated the feasibility of isolating perfluoropolyether oil from a Boron Nitride/PTFE-based lubricating grease matrix with supercritical CO₂ at extraction conditions of 4500 psig and 80° C.

A 300 mL extraction vessel was charged with 174.2 g of a lubricating grease comprised of Boron Nitride, PTFE Micropowder and DuPont Krytox® GPL205 PFPE oil which was placed in two perforated metal baskets in the vessel. The extraction vessel and lubricating grease sample were flushed with CO₂ and then pressurized to 4500 psig with CO₂ at 80° C. The lubricating grease sample was extracted at these conditions and a CO₂ flow rate of 5.2 g/min for 5.0 h with intermittent PFPE oil samples collected from the extract. Table 10 shows the corresponding cumulative extraction yield as a function of the cumulative solvent-to-feed ratio. A total of 92.3 wt % of the 142.9 g of PFPE oil in the starting lubricating grease was recovered in the extract with a total cumulative solvent-to-feed ratio of 8.9. FT-IR analysis verified the recovered PFPE oils to be structurally identical to the original PFPE oils in the starting lubricating grease.

TABLE 10 Solvent-to-Feed Ratio and Extraction Yield Data at 4500 psig and 80° C. for Example 10 Specific Solvent Ratio Extraction Yield (g CO₂/g Lubricating Grease) (wt %) 0.15 17.3 0.30 25.3 0.45 30.8 0.75 41.9 1.04 50.5 1.49 57.1 2.05 64.0 2.88 72.5 3.72 78.3 4.61 82.7 5.79 86.6 6.69 88.4 7.72 89.9 8.91 92.3

Example 11 Extraction Curve at 4500 Psig and 80° C. Using Supercritical CO₂ with Lubricating Grease Comprised of Polyurea Thickener with Both a Polyester and Krytox® 1531 PFPE Oil

This Example demonstrated the feasibility of isolating a polyester and a perfluoropolyether oil from a polyurea-based lubricating grease matrix with supercritical CO₂ at extraction conditions of 4500 psig and 80° C.

A 300 mL extraction vessel was charged with 115.84 g of a lubricating grease comprised of polyurea and a combination of a polyester and DuPont Krytox® 1531 PFPE oil which was placed in two perforated metal baskets in the vessel. The extraction vessel and lubricating grease sample were flushed with CO₂ and then pressurized to 4500 psig with CO₂ at 80° C. The lubricating grease sample was extracted at these conditions and a CO₂ flow rate of 5.2 g/m in for 3.3 h with intermittent PFPE oil samples collected from the extract. Table 11 shows the corresponding cumulative extraction yield as a function of the cumulative solvent-to-feed ratio. A total of 95.9 wt % of the 76.5 g of polyester and PFPE oil in the starting lubricating grease was recovered in the extract with a total cumulative solvent-to-feed ratio of 8.7. FT-IR analysis verified the recovered PFPE oils to be structurally identical to the original PFPE oils in the starting lubricating grease.

TABLE 11 Solvent-to-Feed Ratio and Extraction Yield Data at 4500 psig and 80° C. for Example 11 Specific Solvent Ratio Extraction Yield (g CO₂/g Lubricating Grease) (wt %) 0.22 16.8 0.45 21.9 0.67 25.9 0.89 29.4 1.34 36.4 2.01 46.0 2.99 58.2 4.02 68.7 4.91 76.3 5.81 82.0 6.70 86.9 7.37 89.8 8.71 95.9

Example 12 Extraction Curve at 4500 Psig and 80° C. Using Supercritical CO₂ with Lubricating Grease Comprised of Polyurea/Zinc Oxide Thickener with Both a Polyester and Krytox® 1531 PFPE Oil

This Example demonstrated the feasibility of isolating a polyester and a perfluoropolyether oil from a polyurea and zinc oxide-based lubricating grease matrix with supercritical CO₂ at extraction conditions of 4500 psig and 80° C.

A 300 mL extraction vessel was charged with 119.98 g of a lubricating grease comprised of polyurea, zinc oxide, and a combination of a polyester and DuPont Krytox® 1531 PFPE oil which was placed in two perforated metal baskets in the vessel. The extraction vessel and lubricating grease sample were flushed with CO₂ and then pressurized to 4500 psig with CO₂ at 80° C. The lubricating grease sample was extracted at these conditions and a CO₂ flow rate of 5.2 g/min for 2.8 h with intermittent PFPE oil samples collected from the extract. Table 12 shows the corresponding cumulative extraction yield as a function of the cumulative solvent-to-feed ratio. The 73.8 g of polyester and PFPE oil in the starting lubricating grease was recovered quantitatively in the extract with a total cumulative solvent-to-feed ratio of 7.3. FT-IR analysis verified the recovered PFPE oils to be structurally identical to the original PFPE oils in the starting lubricating grease.

TABLE 12 Solvent-to-Feed Ratio and Extraction Yield Data at 4500 psig and 80° C. for Example 12 Specific Solvent Ratio Extraction Yield (g CO₂/g Lubricating Grease) (wt %) 0.22 24.1 0.43 32.3 0.65 38.0 0.86 42.5 1.29 50.3 1.94 61.1 2.89 73.8 3.88 83.8 4.74 90.0 5.61 94.4 6.68 98.2 7.33 100.0 

What is claimed is:
 1. A process for extracting a perfluoropolyether from lubricating grease, comprising: (a) contacting a solvent comprising a liquid or supercritical carbon dioxide with the lubricating grease, wherein the lubricating grease comprises a thickener and the perfluoropolyether, in an extraction zone to form an extraction solution comprising an extracted perfluoropolyether and wherein the extracted perfluoropolyether comprises unfunctionalized perfluoropolyether and optionally functionalized perfluoropolyether, the functionalized perfluoropolyether if present being present in an amount of no more than 10 wt % based on the total amount of perfluoropolyether; and (b) recovering the extracted perfluoropolyether from the extraction solution; wherein the recovered extracted perfluoropolyether comprises no more than about 2 wt % of the thickener; wherein the yield of the extracted perfluoropolyether is at least about 75 wt %.
 2. The process of claim 1, wherein the recovered extracted perfluoropolyether comprises no more than about 0.1 wt % of the thickener.
 3. The process of claim 1, wherein the thickener is selected from the group consisting of PTFE, FEP, PFA, MFA, ETFE, PCTFE, ECTFE, PVDF, and combinations thereof.
 4. The process of claim 3, wherein the thickener is PTFE.
 5. The process of claim 1, wherein the thickener is selected from the group consisting of talc, silica, clay, boron nitride, titanium dioxide, silicon nitride, and combinations thereof.
 6. The process of claim 1, wherein the thickener is selected from the group consisting of metal soaps, melamine cyanurate, urea, polyureas, polyurethanes, polyolefins, and combinations thereof.
 7. The process of claim 6, wherein the metal soap is selected from the group consisting of lithium soaps, sodium soaps, lithium complex soaps, calcium sulfonates, aluminum soaps, and combinations thereof.
 8. The process of claim 1, wherein the weight ratio of the solvent to the lubricating grease is no more than about
 50. 9. The process of claim 1, wherein the solvent comprises supercritical carbon dioxide.
 10. The process of claim 9, wherein the extraction zone has a temperature and wherein the temperature in the extraction zone is from about 40° C. to about 110° C.
 11. The process of claim 9, wherein the extraction zone has a temperature and wherein the temperature in the extraction zone is from about 70° C. to about 90° C.
 12. The process of claim 9, wherein the extraction zone has a pressure and wherein the pressure in the extraction zone is from about 1500 psig to about 6000 psig.
 13. The process of claim 9, wherein the extraction zone has a pressure and wherein the pressure in the extraction zone is from about 4000 psig to about 5000 psig.
 14. The process of claim 1, wherein the solvent comprises liquid carbon dioxide.
 15. The process of claim 14, wherein the extraction zone has a temperature and wherein the temperature in the extraction zone is from about 25° C. to less than 31.1° C.
 16. The process of claim 1, wherein the yield of the extracted perfluoropolyether is at least about 90 wt %.
 17. The process of claim 1, wherein the recovered extracted perfluoropolyether is further purified by an adsorbing agent. 